It is becoming increasingly difficult, both in terms of cost and availability, to construct conventional open reservoirs for the storage of water. Such reservoirs typically require the construction of a dam across a river, thereby flooding vast expanses of land upstream of the dam while severely curtailing the flow of water downstream from the dam. In light of the increasing value of water and the complexities of the various water laws across different jurisdictions, it is becoming prohibitively difficult to form an open reservoir in this manner. Open reservoirs may also be formed by first excavating a large pit and then filling the pit with water, provided that the reservoir is properly lined to isolate the privately owned water from potential commingling with the public domain water in the same general alluvial deposit. Previously, such open reservoirs could be formed by purchasing the rights to abandoned gravel quarries. However, due to the current high demand for water storage, such opportunities are extremely rare. While it is possible to excavate a large pit for the specific purpose of forming an open water reservoir, such a technique requires a great expense of time and money to purchase the land, form the pit and dispose of the excavated material and soil, assuming that the excavated materials have no intrinsic economic value.
One major disadvantage to open reservoirs is that they preempt any current or future use of the land other than to store water. That is, as additional land surface is devoted to the storage of water in open reservoirs that same land surface is unavailable for alternative uses such as farming or open space. A further disadvantage of storing water in open reservoirs is the high degree of evaporative losses experienced by such reservoirs due to relatively large air/water interface. Specifically, in arid climates (such as those found in the Western United States), open reservoirs are subject to extremely large evaporative losses.
A further unfortunate disadvantage to open reservoirs is that the reservoirs are highly susceptible to contamination. While previous concerns have been limited to accidental chemical spills, petroleum leaks, polluted surface-water runoff, and the like, a more immediate threat is that of intentional contamination as part of a terrorist act. Most municipal water reservoirs comprise unfenced bodies of waters in remote areas and are extremely difficult if not impossible to guard. Furthermore, the construction of fences around existing reservoirs would be expensive and time consuming, and even then the open reservoirs would be susceptible to contamination from the air.
One proposed solution to the above-described disadvantages of open reservoirs is the construction of underground reservoirs where water is stored in the voids or interstices found in alluvial deposits. One such method is described in U.S. Pat. No. 4,326,818, issued to Willis and entitled “Techniques for the Storage of Water.” The Willis patent describes forming an enclosed flexible wall extending vertically downward toward a natural aquiclude or stone base that is impermeable to water. The wall is formed by a grouting process where a grout pipe is first inserted through the soil until the pipe reaches the aquiclude and is then withdrawn while a grout material is injected under pressure from the end of the pipe. The grout material moves away from the injection zone and fills the pores of the formation where it hardens to form a grout “column.” This process is repeated numerous times to form a closed perimeter wall around a defined reservoir boundary. That is, adjacent grout columns are positioned so that there is little or no space between the columns. A second and third round of grout columns are then formed adjacent the first round of columns to form a wall that is said to be substantially impermeable to water. Conventional wells and feed lines are then constructed within the boundary of the grout wall to withdraw and supply water to the reservoir as needed.
The specific reservoir described in the Willis patent suffers from a number of drawbacks. Initially, the grout wall construction technique described by Willis (i.e., pressure-grouting clay or other “flexibilized” materials and allowing the grout to “jel” into place) does not typically form uniform subsurface columns. Rather, the grout material disperses from the end of the grout pipe in an uneven and haphazard manner (i.e., permeating different radial distances away from the grout pipe) as the grout pipe is retracted toward the surface. The uneven nature of the grouting process tends to form vertical sand seams between the grouted columns at the outer boundary of the pressure injection. These sand “lenses” or areas of high permeability formed between adjacent grout “columns” result in grout walls that do not form substantially impermeable water barriers and that are susceptible to relatively high levels of water leakage or seepage. Additionally, it is not possible to key the grouted in-situ “columns” into the bedrock or other impermeable basement rock that defines a bottom surface of the underground reservoir. Rather, a small horizontal layer typically remains between the bottom ends of the various grout columns and the bedrock so that water may escape the reservoir through this gap between the wall and the bedrock, where the hydrostatic pressure is at its greatest level. Indeed, between the inability to form a solid impermeable wall using the grout technique, and the inability to firmly tie the grout columns to the bedrock defining the lower surface of the reservoir, the water leakage rates of a reservoir built according to the technique of the Willis patent would be prohibitively high.
A second drawback to the technique of the Willis patent is the use of conventional wells for charging and extracting water from the underground reservoir. Specifically, such wells are relatively inefficient when it comes to rapidly charging the reservoir with water during periods of surplus water, such as during a Spring runoff. The same wells are similarly inefficient with respect to withdrawing water at a desired high rate during periods when the water level within the reservoir is low. That is, because the typical groundwater flow past the well is prevented within the confines of the subsurface reservoir (and thus the water within the reservoir is not pressurized to the same degree as would be found in a natural aquifer), conventional vertical wells are unsatisfactory when it comes to extracting water at a desired rate from the underground reservoir.
A further problem associated with the underground reservoir described in the Willis patent is that there is no recognition of the problems associated with the construction of the massive subsurface walls. Specifically, the installation of any subsurface wall on the scale of that required to form an underground reservoir tends to form a dam to the normal flow of groundwater so that water levels on the upstream or “high” side of the reservoir wall will tend be higher than historic average levels, while the opposite condition (i.e., lower than average water levels) will be found on the downstream or “low” side of the reservoir. Such artificial changes to the historic water table can have severe adverse impacts on neighbors in the region. For example, neighbors on the high side of a subsurface reservoir may experience flooded basements, while neighbors on the low side will experience a dearth of water such that alluvial wells may run dry.
Thus, while the Willis patent describes one theoretical design for a subsurface reservoir, the specifics of the Willis reservoir are not feasible due both to the inability to form a water-tight reservoir and the further inability to efficiently recharge and extract water from the reservoir. Additionally, the grout wall construction techniques described in the Willis patent are prohibitively expensive (costing $40-$200 per square foot of barrier), particularly when used on the scale required for an underground reservoir. Furthermore, the Willis patent does not account for the environmental impact that will be caused by the construction of the potentially massive subsurface walls. Thus, an improved subsurface reservoir and method for storing water is needed that will address the shortcomings of the Willis design. It is with respect to these and other background considerations, limitations and problems that the present invention has evolved.